Several types of furnaces are used in the materials processing industry. For example, one type of furnace used for thermal processing in the semiconductor industry is a batch furnace. Batch furnaces typically include a large area that supports and thermally processes multiple substrates simultaneously. Batch furnaces are relatively simple because they have no internal moving parts. However, they are typically energy inefficient and have relatively low throughput and long processing times. In addition, batch furnaces typically can not generate complex or rapid thermal profiles that are required for some applications.
Another type of furnace used in the industry for thermal processing is a belt furnace. Belt furnaces typically comprise an elongated passageway and a plurality of heating elements positioned at locations along the passageway. In operation, substrates are loaded onto a belt or conveyor and transported through the passageway in proximity to the plurality of heating elements at a predetermined speed.
Typically, each of the plurality of heating elements is individually controllable to achieve a predetermined thermal profile. The rate of transport though the passageway is also controllable. Consequently, belt furnaces can achieve a predetermined thermal profile that can be both complex and rapid. Belt furnaces can achieve a significantly higher ramp rate compared to batch furnaces. For example, belt furnaces can heat a substrate with a ramp rate greater than 100 degrees per minute, and cool a substrate with a ramp rate greater than 30 degrees per minute. Such ramp rates are required for certain manufacturing processes, such as reflow processes.
Belt furnaces are generally more energy efficient and simpler to use compared to batch furnaces and can be used to generate complex and rapid thermal profiles. In addition, belt furnaces are less expensive than batch furnaces. However, belt furnaces have a relatively large footprint, and therefore take up valuable clean room space. Belt furnaces also have a long warm-up time, and are relatively difficult to automate. In addition, it is difficult to control the ambient temperature within a belt furnace.